Download text - Systems Neuroscience Course, MEDS 371, Univ. Conn. Health

Graduate School Systems Neuroscience, MEDS 5371
2013
Diencephalon anatomy
1. READING
Purves, 4th Ed.
INTRODUCTION
The diencephalon is positioned on both sides of the third ventricle, and can be identified by
the third ventricle, thalamus, optic chiasm, and mammillary bodies. The diencephalon is
divided into several parts: dorsal thalamus (largest part), hypothalamus, epithalamus,
metathalamus (MGN, LGN), and subthalamus. The ventral and medial part of the
diencephalon is the hypothalamus that contains numerous nuclei; they maintain
homeostasis through regulating the function of the autonomic nervous system. On the base
of the brain (ventral side) parts of diencephalon, from rostral to caudal direction, can be
identified: optic chiasm, infundibulum (for the hypophysis or pituitary gland) and mammilary
bodies. The ventral and lateral part of the diencephalon is the subthalamic nucleus,
functionally a part of Basal ganglia circuitry and will be discussed with Basal ganglia.
Epithalamus is the posterior wall of the third ventricle and consists of pineal gland,
habenula, posterior commissure. Pineal gland has a role in circadian cycle. Habenula
(habenular nuclei) receive inputs through stria medullaris from septal region; outputs are
sent to many midbrain areas involved in releasing dopamine, norepinephrine, and
serotonin. Habenula has a role in pain processing, sleep-wake cycles, stress responses,
and processing negative rewards.
During development optic vesicles which form the eyes are parts of the
diencephalon. Thus, neural portion of the retina is a part of CNS.
Thalamus, also called the dorsal thalamus, is the largest part of the diencephalon. It is
often considered a gateway to cerebral cortex. All pathways coming from lower parts of the
CNS before reaching cerebral cortex stop in the thalamus. Thalamus is an integration
center- it receives reciprocal connections from the cortex, cerebellum and basal ganglia. It
contains several groups of nuclei that are designated for various functions (see Table at the
end of the syllabus).
Nuclei Related to sensory function
VPL- Ventro-posterior-lateral nucleus- receives sensory information from the body and
conveys them to somato-sensory cortex (postcentral gyrus). These sensations are for touch,
two point discrimination, and vibration coming through Medial Lemniscus, as well as for pain
and temperature coming through ALS (spino-thalamic tr). Since both of these pathways are
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crossed they convey information from the opposite side of the body to the somato-sensory
cortex.
VPM –Ventro-posterior- medial nucleus has similar function for head and face. Sensory
informations are coming mainly through the ventral trigemino-thalamic tract, which is
crossed.
Special sensory nuclei- Metathalamus
Lateral geniculate nucleus (LGN) is a relay station in the visual pathway, receiving fibers
from the optic nerve (II cranial nerve) and projecting as the visual radiation to the visual
cortex in the occipital lobe.
Medial geniculate nucleus (MGN) is a relay station in the auditory pathway receiving
auditory signals from ears through cochlear nerve (part of VIII cranial nerve) and lateral
lemniscus. From the MGN this information is conveyed to the auditory cortex in the temporal
lobe.
Nuclei Related to Motor function
VA and VL (ventro-anterior and ventro-lateral) nuclei receive inputs from the cerebellum
and the basal ganglia and connect to the motor and premotor cortex, having a role in motor
function.
Nuclei Related to the Limbic System
MD- Mediodorsal nucleus is positioned medially, close to ventricular surface and is
connected to prefrontal cortex; it receives connections from the amygdala, globus pallidus
and midbrain reticular formation. It has a function in memory (see below).
AN-Anterior nucleus is a part of limbic system. It receives inputs from the mammilary bodies
and sends fibers to the cingulate gyrus.
Centrum medianum (CM)- receives inputs from from Globus Pallidus and sends outputs to
the Motor cortex. It is also included in a pain pathway.
Pulvinar- is the most caudal thalamic nucleus. It receives projections from the auditory,
somatosensory and visual cortex regions. It is involved in visual attention, suppression of
irrelevant stimuli and utilizing information to initiate eye movements.
Reticular and interlaminar nuclei- connected to reticular formation and cerebral cortex, thus
they can act as part of ascending activation system (influence level of alertness &
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consciousness). Damage to the thalamus can lead to permanent coma.
Intralaminar nuclei are in the pain pathway.
Mammilary bodies are part of the limbic system and will be discussed again later. They
receive information from the hippocampus via fornix (fiber bundle) and from the amygdala.
Information is transferred from the mammilary bodies by Mammilothalamic tract to the
Anterior nucleus of the thalamus (AN). This nucleus also receives branches from the Fornix,
and further projects to the prefrontal cortex and cingulum (all parts of Limbic system).
Subthalamic Nucleus is position bellow the thalamus. Functionally it is a part of Basal
ganglia.
Thalamic nuclei, their connections & functions
Part of the
Nuclei
Connections
Functions
thalamus
Anterior
part
Anterior thalamic
nuclei
Medial part Dorso – medial
1.
Mammillo – thalamic tract
2.
Hypothalamus
Emotional tone
Mechanism of recent
3.
Cingulate gyrus
memory
1.
Prefrontal cortex
Integration of somatic,
2.
Hypothalamus
visceral & olfactory
information and relate those
information to one’s
emotional feelings &
subjective states
1.
Lateral
part
Ventral tier
1.Ventralanterior
VA
2.Ventral lateral
VL
3. VPM
1.
RF
2.
Substantia nigra
3.
Corpus striatum
4.
Premotor cortex
1.
Cerebellum
2.
Red nuclei
3.
RF
4.
Substantia nigra
5.
Corpus striatum
6.
Premotor cortex
1.
Trigeminal lemnisci
Influence the activities of
the motor cortex
Relays common sensations
to consciousness
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4. VPL
1.
Medial & spinal
lemnisci
Other
nuclei
1. Intra laminar
2.
cortex (3, 2 & 1)
1.
RF
2.
Spino – thalamic tract
3.
Trigemino – thalamic tract
2.Midline
RF
Influence the level of
alertness & consciousness
Unknown
3. Reticular
4. Medial
geniculate body
1.
Inferior colliculus
2.
Lateral lemnisci from both
MGB
Hearing
ears (Predominantly from
the contra lateral ear)
3.
Efferent – Auditory
radiation to superior
temporal gyrus
5.Lateral
geniculate body
LGB
1.
2.
Visual information from the
opposite visual field
Efferent – Optic radiation
Optic tract
to visual cortex of the
occipital lobe
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